Heat exchanger

ABSTRACT

Oil passages  113  through which oil passes are formed with plates  111, 112  composed of aluminum or an aluminum alloy in an oil cooler, according to the present invention, that is a heat exchanger with an extended life. Moreover, fins  123   a  composed of a material having a corrosion potential more negative than those of the plates  111, 112  are arranged in cooling water passages  123  through which cooling water, for exchanging heat with oil, passes. A sacrificial corrosive layer  301  having a corrosion potential more negative those of the plates  111, 112  and the fins  123   a  is formed on each of the surfaces on the sides of the cooling water passages  123  of the plates  111, 112.  As a result, the sacrificial corrosive layer  301  is preferentially corroded, and not only the plates  111, 112  but also the fins  123   a  can be protected. Consequently, the pressure-proof strength of the oil cooler can be maintained, and the product life can be improved.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 09/799,456 filed on Mar. 6, 2001, the contents beingincorporated therein by reference. This application claims the benefitof Japanese Patent Application No. 11-223479, filed Aug. 6, 1999 and No.2000-223227 filed Jul. 25, 2000, the contents being incorporated thereinby reference, and a continuation of PCT/JP00/05268.

FIELD

The present invention relates to a heat exchanger, and more specificallyto the constitution, and joining by brazing, of heat exchanger parts.The heat exchanger of the present invention can be effectively appliedto an oil cooler for cooling engine oil and hydraulic oil (ATF) for theautomatic transmissions of automobiles (hereinafter merely referred toas oil) and the like.

BACKGROUND

Radiators and condensers have been made of aluminum for use as heatexchangers for air conditioners for automobiles, etc. Such a heatexchanger can be manufactured by alternately laminating a plurality oftube elements (hereinafter abbreviated to tubes) each composed of abrazing sheet that is made of aluminum or aluminum alloy and a pluralityof fins and brazing, for example, vacuum brazing, the laminated tubeelements and fins.

For such a heat exchanger, a sacrificial corrosive material showing acorrosion potential more negative than that of the tube surface materialis used as the fin material in order to improve the corrosionresistance. It is known that the fins are then preferentially corrodedin comparison with the tubes to protect corrosion of the tubes.

An oil cooler that exchanges heat between engine oil or the like andengine cooling water generally has a structure in which a plurality oflaminated plates are accommodated within a casing. The spaces formed bythe plurality of laminated plates become oil passages through which theoil passes. A space formed by the space outside the oil passages and thecasing becomes cooling water passages through which the cooling waterpasses. In addition, inner fins are arranged in the oil passages toimprove the heat exchangeability.

When an oil cooler having such a structure is to be made of aluminum, itis desirable also to provide inner fins as an additional strengtheningstructure in the cooling water passages to provide pressure-proofstrength. However, when a heat exchanger has such a constitution inwhich fins are preferentially corroded as that of the aluminum-made oneexplained above, the fins arranged in the cooling water passages arefirst corroded, and a required pressure-proof strength cannot bemaintained. As a result, there arises the problem that the product lifeof the oil cooler itself is shortened.

SUMMARY

The present invention has been achieved in view of the problemsmentioned above. An object of the present invention is to suppressshortening of the product life caused by corrosion.

In order to achieve the object, the present invention provides a heatexchanger for carrying out a heat exchange between oil and coolingwater, which comprises:

a plurality of first plates and a plurality of second plates that arecomposed of aluminum or an aluminum alloy, and that are alternatelylaminated and joined by brazing;

oil passages which are each formed between one surface of one of thefirst plates and one surface of one of the second plates that isarranged to face the one surface of the first plate, and through whichoil passes;

cooling water passages which are formed between the other surface of theone of the first plates and one surface of one of the second plates thatis arranged to face the other surface of the first plate, and throughwhich cooling water passes; and

cooling water side fins brazed to the inner wall surfaces of the coolingwater passages, wherein the cooling water side fins are composed ofaluminum or an aluminum alloy having a corrosion potential more negativethan those of the core layers of the first plates and the second plates,and a sacrificial corrosive layer having a corrosion potential morenegative than those of the core layers of the first plates and thesecond plates and the cooling water side fins is formed on each of theabove other surface of the first plate and second plate that faces theabove other surface of the first plate.

That is, for the heat exchanger (oil cooler) of the present invention,the sacrificial corrosive layers having a corrosion potential morenegative than those of the first and the second plates and the fins onthe cooling water sides are preferentially corroded. As a result, notonly the first and the second plates but also the fins on the coolingwater passage sides can be protected from corrosion. Consequently, evenwhen aluminum or an aluminum alloy having a low strength compared withthose of conventional materials is used as a material for the heatexchanger (oil cooler), the pressure-proof strength of the heatexchanger (oil cooler) can be maintained. Moreover, a material having acorrosion potential more negative than that of the core layers of thetubes is used as the fin material of the fins on the cooling waterpassage sides. Therefore, even when corrosion proceeds in the heatexchanger, the fins on the cooling water sides are preferentiallycorroded in comparison with the first and the second plates forming thecooling water passages and oil passages; as a result, the period forwhich the first and second plates can be used without damage can beprolonged, and the product life can thus be extended.

DRAWINGS

FIG. 1 is a sectional view of an oil cooler according to a firstembodiment of the present invention.

FIG. 2 is a sectional view showing main parts of the present invention.

FIG. 3 is a sectional view of an oil cooler according to anotherembodiment of the present invention.

DETAILED DESCRIPTION

Embodiments according to the present invention will be explained belowby making reference to drawings. FIG. 1 is a sectional view of an oilcooler 100 that is one embodiment to which the constitution of the heatexchanger of the present invention is applied.

The oil cooler 100 is mounted on the wall surface of a cylinder block, acrankcase or a transmission main body for a driving engine (not shown).The oil cooler carries out a heat exchange between engine cooling water(hereinafter abbreviated to cooling water) and oil, such as engine oiland hydraulic oil (ATF) for automatic transmission, to cool the oil.

Reference numeral 110 indicates a heat-exchanger core (hereinafterabbreviated to a core) that carries out a heat exchange between the oiland the cooling water. The core 110 is formed by laminating a pluralityof plates 111 and a plurality of plates 112 (corresponding to firstplates and second plates, respectively) that are press formed in advanceto have recesses and protrusions with predetermined shapes for improvingthe heat exchangeability, in the thickness direction of the plates 111and the plates 112 themselves. In addition, spaces, which will beexplained below, and through which oil passes are formed in the interiorbetween one of the plates 111 and the corresponding plate 112, and theplates 111 and the plates 112 function as tube elements.

Reference numeral 120 indicates an approximately cylindrical casing thataccommodates the core 110. A closed space that accommodates the core 110is formed within the casing 120 by blocking openings 120 a, 120 b on tworespective sides in the axial direction of the casing 120 (top andbottom sides in FIG. 1) with a disk-like top face plate 130 and adisk-like bottom face plate 140, respectively. A cooling water inletside pipe 121 a and a cooling water outlet side pipe 122 a are providedto the respective cylindrical wall portions of the casing 120. Thecooling water flows in through an inlet 121, and flows out through anoutlet 122 after carrying out a heat exchange between the cooling waterand the oil in the core 110.

Spaces 113 formed (partitioned) by the plates 111, 112 form passages(fluid passages) through which the oil passes. On the other hand, ofspaces formed by the casing 120 and the first and second plates 130,140, spaces (spaces within the casing 120) 123 other than the spaces 113(hereinafter referred to as the oil passages 113) form passages throughwhich the cooling water passes (hereinafter referred to as cooling waterpassages 123). Spaces formed along the laminated tube elements eachformed by a pair of plates 111, 112 become part of the cooling waterpassages 123 through which the cooling water passes.

In addition, inner fins 113 a, 123 a having offset shapes that promote aheat exchange between the oil and cooling water are provided within therespective passages 112, 123. Moreover, oil passages 143, through whichthe oil passes, are formed in the plate 140.

Furthermore, reference numeral 150 indicates a bearing surface platejoined to the second plate 140 by brazing. Of the two side surfaces ofthe bearing surface plate 150, the side surface opposite to the secondplate 140 (the side surface contacted with the wall surface of thecylinder block or crankcase) 151 has an O-ring groove 152 in which anO-ring 161 made of an acrylic rubber is placed. The gap between thesurface 151 (hereinafter referred to as the seal surface 151) and thewall surface of the cylinder block or crankcase is sealed therewith.

In order to ensure a predetermined sealability, the O-ring groove 152and sealing surface 151 are machine finished to have a predeterminedsurface roughness (a mean surface roughness for 10 points R_(z) (JISB0601) of up to 12.5 z in the present embodiment).

In addition, reference numeral 153 indicates a by-pass hole that makesthe oil inlet side communicate with the oil outlet side in the oilcooler 100 while the oil from the inlet side is making a circuit roundthe core 110 and flows out of the oil outlet side. The by-pass hole 153has a given hole diameter to prevent the oil from excessively making acircuit round the core 110 and excessively flowing out toward the oiloutlet side (excessive pressure loss). Reference numeral 141 indicatesan aluminum third plate that is contacted with the lowest plate 112 toreinforce the plate 112.

In addition, the plates 111, 112 are formed from aluminum or an aluminumalloy such as Al—Mn—Cu-based alloy. As shown in FIG. 2, of the surfacesof the plates 111, 112, the surfaces facing the cooling water passages123 are each clad in a sacrificial material that is formed from analuminum alloy such as an Al—Zn based alloy and that has a more negativecorrosion potential than the materials of the plates 111, 112 to form asacrificial corrosive layer 301. On the other hand, a core layer 1230 ofthe inner fin 123 a is formed from aluminum or an aluminum alloy, andthe surfaces of the core layer are each clad with a clad layer 1231composed of a brazing material. In addition, a material such as anAl—Mn-based alloy having a corrosion potential more negative than thatof the material of the plates 111, 112 and more positive than that ofthe sacrificial corrosive layer 301 is used for the core layer 1230 ofthe inner fin 123 a.

If the corrosion potential of the cooling water side fin is 5 to 50 mVhigher than those of the sacrificial corrosive layers of the firstplates and the second plates, corrosion of the sacrificial corrosivelayers is accelerated and, accordingly, the sacrificial layers are wornsoon, and the anticorrosion property thereof is reduced. This is notpreferable.

For the oil cooler 100 in the present embodiment, the sacrificialcorrosive layers 301 with respect to the plates 111, 112 and the innerfin 123 a are on the respective surfaces that face the cooling waterpassage 123 of the plates 111, 112. As a result, the sacrificialcorrosive layers 301 are preferentially corroded in comparison with theplates 111, 112 and the inner fin 123 a, and the plates 111, 112 and theinner fin 123 a are prevented from corrosion. Therefore, the life of theinner fin 123 a can be extended and the fin can maintain a requiredpressure-proof strength. Moreover, the heat exchanger can maintain apredetermined heat exchangeability because the inner fins 123 a areprotected.

Furthermore, even when the corrosion proceeds, further, the inner fins123 a are corroded in preference to the plates 111, 112 because theinner fins 123 a are composed of a material having a corrosion potentialmore negative than those of the plates 111, 112. Accordingly, the periodafter which the corrosion of the plates 111, 112 takes place can beprolonged, and the product life can be extended.

In addition, an explanation of an oil cooler having no filter forcleaning oil has been made in the above embodiment. However, it isneedless to say that the present invention can also be applied to an oilcooler integral with a filter in which a filter 200 is integrated intoan oil cooler 100 as shown in FIG. 3. In addition, in FIG. 3, referencenumeral 160 indicates a bearing surface plate on the filter side.

Moreover, an oil cooler having the core 110 formed by laminating aplurality of the plates 111 and a plurality of the plates 112 has beenexplained in the above embodiments. However, the core may have anothershape. Moreover, there is no specific limitation on the shapes of theplates and fins when the present invention is to be applied.

Furthermore, although the present invention has been applied to oilcoolers for automobiles in the above embodiments, it can also be appliedto other vehicles such as motorcycles.

Still furthermore, although an explanation has been made of a mode inwhich the inner fins 123 a have a cladding of a brazing material in theabove embodiments, the same effects as in the above embodiments can beobtained even when a constitution is adopted wherein bearing parts areused as the inner fins 123 a, the plates 111 and the plates 112 formingtubes are clad in a sacrificial material, and the plates are furtherclad in a brazing material.

Although a cup-like tank T is formed by blocking one end in the axialdirection of the casing 120 with the first plate 140 in the aboveembodiments, a tank may also be integrally formed by a deep drawing(pressing) or a similar procedure.

The product life of the heat exchanger of the present invention can beextended by considering the corrosion potentials of materials formingrespective parts in the heat exchanger, and providing sacrificialcorrosive layers that are preferentially corroded.

Moreover, a required pressure-proof strength and a desired heatexchangeability of the heat exchanger of the present invention can bemaintained by considering the strength of each of the part materials inthe heat exchanger.

1. A heat exchanger for carrying out a heat exchanger between oil andcooling water, which comprises: a plurality of first plates and aplurality of second plates that are composed of aluminum or an aluminumalloy, and that are alternately laminated and joined by brazing; oilpassages which are each formed between one surface of one of the firstplates and one surface of one of the second plates that is arranged toface the one surface of the first plate, and through which oil passes;cooling water passages which are each formed between the other surfaceof the one of the first plates and one surface of one of the secondplates that is arranged to face the other surface of the first plate,and through which cooling water passes; cooling water side fins brazedto the inner wall surfaces of the cooling water passages, wherein thecooling water side fins are composed of aluminum or an aluminum alloyhaving a corrosion potential more negative than those of the core layersof the first plates and the core layers of second plates, and asacrificial corrosive layer having a corrosion potential more negativethan those of the core layers of the first plates, the core layer of thesecond plates and the cooling water side fins is formed on each of theother surface of the first plate and the other surface of the secondplate that faces the other surface of the first plate; and the corrosionpotential of the cooling water side fins is 5 to 50 mV higher than thoseof the sacrificial corrosive layer of the first plates and thesacrificial corrosive layer of the second plates.
 2. A heat exchangeraccording to claim 1, wherein the heat exchanger is an oil cooler.
 3. Alaminated type heat exchanger comprising: a plurality of first platesand a plurality of second plates alternately laminated to form oilpassages through which oil flows and cooling water passages throughwhich cooling water flows alternately and joined by brazing; each of theoil passages is formed between one surface of the first plate and onesurface of the second plate; each of the cooling water passages isformed between the other surface of the first plate and the othersurface of the second plates; and a cooling water side fin brazed toeach of the other surfaces of the first plates and each of the othersurfaces of the second plates; wherein each of the first plates and thesecond plates comprises a laminated layer of a core layer made ofaluminum or aluminum alloy completely covered by a sacrificial corrosivelayer disposed on the other surface of the first plate and on the othersurface of the second plate; the sacrificial corrosive layer is made ofa material of which an electrical potential is more negative than anelectrical potential of the core layers and the cooling water side fins;the cooling water side fins are made of a material of which anelectrical potential is more negative than the core layers; and thecorrosion potential of the cooling water side fins is 5 to 50 mV higherthan those of the sacrificial corrosive layer of the first plates andthe sacrificial corrosive layer of the second plates.
 4. A heatexchanger according to claim 3, wherein the heat exchanger is an oilcooler.